Low dew point air dehumidification assembly

ABSTRACT

A dehumidifier apparatus ( 10 ) to provide low humidity air to an enclosure. The apparatus ( 10 ) includes an outer housing ( 11 ) providing six air passages ( 12  to  17 ). Also located in the outer housing ( 11 ) is a heat exchanger ( 22 ) that provides two air paths between which heat is exchanged. The apparatus ( 10 ) further includes coils ( 27, 28  and  29 ) as well as a motorised damper ( 18 ) and fan ( 19 ). The apparatus ( 10 ) further includes a refrigeration circuit ( 73 ) and controller ( 30 ), with the controller ( 30 ) operating the damper ( 18 ), fan ( 19 ) and circuit ( 73 ) to provide low dew point dehumidified air.

FIELD

The present invention relates to a dehumidification apparatus that uses refrigeration to cool air to a temperature low enough to cause its water moisture content to fall below 5 grams water per kilogram of air.

BACKGROUND OF THE INVENTION

There are numerous building and industrial process applications that require the relative humidity of air within an enclosure to be maintained at a very low level. In some instances, the specified relative humidity requires the absolute humidity of the air to be reduced to less than 5 grams of water vapour per kilogram of dry air (5 gms/kg).

As air is cooled its relative humidity rises because the capacity of the air to absorb water vapour decreases with a fall in temperature. The temperature at which the air reaches 100% relative humidity and becomes saturated for any given absolute humidity is called the dew point. The higher the air absolute humidity, the higher the dew point temperature.

As the air temperature falls below its dew point, water vapour condenses from the air lowering its absolute humidity level. Air has to be reduced to a temperature below 4 degrees centigrade (4° C.) before its absolute humidity falls below 5 gms/kg.

There are two principal methods to reduce the absolute humidity of air to a lower level. Firstly, the air can be cooled to a temperature below the dew point corresponding with the specified absolute humidity or, secondly, air can be placed in contact with a desiccant material that chemically attracts and retains the water vapour in the desiccant.

Present air dehumidifiers either cool the air by passing it over a cold refrigeration evaporator coil causing the water vapour to condense from the air or pass the air through a desiccant (solid or liquid) to attract and retain the water. In some commercial dehumidifiers, a combination of both methods can be employed. Each method has its advantages and disadvantages.

Desiccant dehumidification is generally adopted when an absolute humidity of less than 6 gms/kg is specified. Cooling air by passing it over an evaporator in a refrigeration circuit to reach a DP of 4° C. will require the evaporation of the refrigerant to occur at a temperature approaching or below 0° C. Water that comes in contact with this cold evaporator coil will freeze and cause ice to build up on the evaporator coil lowering the efficiency of the refrigeration system and eventually cause the refrigeration system to shut down completely. To prevent this, the refrigeration system must be reversed periodically to heat and de-ice the evaporator coil. This de-ice procedure is acceptable in a refrigeration or air conditioning application where the space temperature can be maintained during the de-ice period. However, a disadvantage is that it is unacceptable where a constant supply of dehumidified air is required. This de-ice downtime period can be avoided by duplicating all or part of the refrigeration cooling circuit.

Cooling air that is both hot and humid to reach a low absolute humidity level has the disadvantage that it is extremely energy intensive as:

-   -   a. the amount of refrigeration work required to lower the air         temperature from its ambient condition to the low temperature         required is substantial; and     -   b. the efficiency of the refrigeration process or coefficient of         performance (COP) is relatively low because the difference         between the evaporating and condensing pressures is high.

Desiccant dehumidification does not require lowering the air temperature to such low levels with refrigeration, but it does require significant heat energy to regenerate the desiccant. Moisture must be removed from the desiccant (regeneration) which is generally achieved by passing very hot air over the desiccant so that it gives up moisture to this hot dry airstream. Most desiccant dehumidification systems are based on a wheel to which a desiccant is attached. The wheel rotates through the process moist air stream to attract water vapour from the process air and continues to rotate through a second hot dry exhaust air stream that causes the desiccant to give up its retained moisture to the hot dry exhaust air before rotating again to the moist process air stream. Various combinations of wheels and air paths are employed in desiccant dehumidifiers, however, the disadvantage is that they all need hot dry air to ensure adequate regeneration of the desiccant to enable it to continue to attract and hold more moisture.

Some desiccant dehumidification systems employ refrigeration circuits to cool the process air before it passes through the wheel. An advantage is that this cooling causes the air relative humidity to rise until it reaches saturation and condensation commences to remove part of the entrained water vapour. The second benefit of air cooling before it is bought in contact with the desiccant is that the water absorption performance of the desiccant improves as the air relative humidity rises. The waste refrigeration heat from this refrigeration pre-cooling process is used to partly heat the regeneration airstream. The addition of a refrigeration system increases the overall efficiency of the desiccant dehumidifier but hot regeneration air is still needed to maintain the desiccant performance.

OBJECT

It is the object of the present invention to overcome or substantially ameliorate at least one of the above disadvantages.

SUMMARY OF INVENTION

There is disclosed herein a dehumidification apparatus including:

a primary heat exchanger having a first air path and a second air path, with the heat exchanger providing for transfer of heat between air passing along the two paths;

a first air passage that directs input air entering the dehumidifier into the heat exchanger;

a second air flow passage that receives the input air after passing through the heat exchanger first path;

an airflow regulator, operatively associated with the first air passage and upstream of the heat exchanger, to selectively direct at least part of the input air from the first air passage to the second air flow passage so that air so directed bypasses the heat exchanger;

a first air cooling heat exchanger to which air is directed by the second air flow passage;

a second air cooling heat exchanger;

a third air flow passage that directs air leaving the first air cooling heat exchanger to the second air cooling heat exchanger;

a fourth air flow passage that directs air leaving the second air cooling heat exchanger to the second air flow path of the heat exchanger;

an air heating heat exchanger;

a fifth air flow passage that directs the air leaving the second air flow path of the heat exchanger to the air heating heat exchanger;

an air movement device that causes the air to pass through the dehumidifier from an air inlet to an air outlet, with the inlet delivering air to the first passage, and the outlet receiving air from the air heating heat exchanger; and

a controller operatively associated with the air flow regulator, air movement device, first air cooling heat exchanger, second air cooling heat exchanger, and air heating heat exchanger, so that air leaving the air outlet has a required absolute humidity and temperature.

Preferably, the air movement device is a fan or fans located in the fifth or sixth air passage but downstream of the heat exchanger second path, each fan being operable to move air through the passages and heat exchanger paths.

Preferably, the airflow regulator is a motorized damper.

Preferably, the controller operates the air flow regulator to govern the flow rate of air delivered to the heat exchanger first path, and the second air flow passage.

In one preferred form, the first air cooling heat exchanger receives chilled water.

Preferably, the second air cooling heat exchanger is an evaporator in a refrigeration circuit.

In an alternative preferred form, the first air cooling heat exchanger is a refrigerant evaporator.

Preferably, the air heating heat exchanger is a refrigerant condenser.

In a further preferred form, the assembly includes a refrigerant circuit including a evaporator providing the second air cooling heat exchanger, and a condenser providing the air heating heat exchanger.

Preferably, the refrigeration circuit includes a further condenser, arranged in parallel with the air heating heat exchanger to discharge excess heat from the apparatus.

Preferably, moisture is inhibited from passing between the two air paths in the heat exchanger.

Preferably, the second air cooling heat exchanger is mounted horizontally to aid in draining condensed water or specially constructed for vertical installation.

BRIEF DESCRIPTION OF DRAWINGS

Preferred forms of the present invention will now be described by way of example with reference to the accompanying drawings wherein:

FIG. 1 is a schematic side elevation of a dehumidifying assembly to lower the air temperature sufficiently to reduce the water vapour content in air to less 5 gms/kg absolute humidity;

FIG. 2 is a schematic illustration of the first cooling coil refrigerant circuit; and

FIG. 3 is a schematic illustration of the second cooling coil refrigerant circuit.

DESCRIPTION OF EMBODIMENTS

In the accompanying drawings there is schematically depicted a dehumidifier apparatus 10 (air cooling and heating assembly) to provide low humidity air to an enclosure.

The apparatus 10 includes an outer housing 11 providing six air passages 12, 13, 14, 15, 16, and 17. The first air passage 12 is separated from the second passage 13 and third passage 14 by a divider panel 20. The second air passage 13 is separated from the third passage 14 and fourth passage 15 by a divider panel 21.

The divider panel 20 includes a motorized damper 18 which allows air to enter the second air passage 13 upstream of the first cooling coil 27 (first cooling heat exchanger) without passing through the first air path 12 or the first air path of the heat exchanger 22.

At the downstream end of air passage 12 is an air to a primary air heat exchanger 22 to pre-cool the air before reaching the first air cooling coil 27 and re-heat the air after leaving the second air cooling coil 28. As an example, the heat exchanger 22 may be a heat exchanger as described in any one of Australian Patents 2004215315, 2005266840, 2008299568 or 2008295434.

The heat exchanger 22 has a first inlet wall portion 23, and a second inlet wall portion 25. It also has a first outlet wall portion 24 and a second outlet wall portion 26. Air travels from the inlet portion 23 to the outlet portion 24 of heat exchanger 22 along a first path, while air flows from the inlet portion 25 to the outlet portion 26 of the heat exchanger along a second path. The heat exchanger is constructed so that moisture is not transferred between the first and second paths thereof. For example, partitioned walls within the heat exchanger 22 could be formed of a foil or plastic type material so as to conduct heat but prevent the transfer of moisture.

The air duct passage 13 extends from the heat exchanger wall portion 24 to a first air cooling coil 27. Air duct passage 14 extends from the first cooling coil 27 to the second air cooling coil 28. Air duct passage 15 extends from the second air cooling coil 28 (second cooling heat exchanger) to the heat exchanger wall 25. Air duct passage 16 extends from the heat exchanger wall 26 to an air heating coil 29. Air duct passage 17 extends from heating coil 29 to the outlet of the dehumidifier assembly.

Located in air passage 16 or 17 is a fan (or fans) 19 that are operable to cause air to pass through the dehumidifier from entry 71 to exit 72. Hot moist air enters air passage 12 and is directed to the heat exchanger wall 23 passing through the heat exchanger first path from wall 23 exiting at the heat exchanger at wall 24. Air travels from heat exchanger wall 24 to the first air cooling coil 27 through air passage 13 where it is cooled to an intermediate temperature between its temperature when exiting heat exchanger wall 24 and its specified dew point temperature. Air leaving the first air cooling coil 27 travels to the second air cooling coil 28 through passage 14 where it is further cooled to reach its specified dew point temperature and absolute humidity. Cold dehumidified air leaving the second air cooling coil 28 travels to the heat exchanger wall 25 through passage 15. Cold dehumidified air entering the second path of the heat exchanger 22 at wall 25 and leaving at wall 26 is heated by the warm air travelling through the first path of the heat exchanger 22 as it travels from wall 23 to wall 24. Warm moist air travelling through the first path of the heat exchanger 22 from wall 23 to wall 24 is simultaneously cooled by the cold dehumidified air travelling through the second path of the heat exchanger 22 from wall 25 to wall 26.

When the air travelling through the second path of the heat exchanger 22 exits at wall 26 above its specified temperature, the controller 30 causes the motorized damper 18 to open and allow warm moist air to travel from passage 12 to passage 13 thereby reducing the amount of warm air reaching the first path of the heat exchanger 22 at wall 23. A reduction in the volume of warm airflow through the first path of the heat exchanger 22 reduces the amount of heat available to be transferred from the first path of the heat exchanger 22 to air in the second path of the heat exchanger 22 lowering the temperature of the air when exiting the second path of the heat exchanger 22 at wall 26. The amount of air allowed to pass through the motorized damper 18 is varied to deliver the specified temperature of air exiting the heat exchanger 22 at wall 26.

When the air entering the dehumidifier assembly 10 through passage 12 (entry 71) is at a lower ambient temperature and humidity, the heat transferred from the air in the first path of the heat exchanger 22 to the air in the second path of the heat exchanger 22 may not be sufficient to raise the air temperature exiting at wall 26 to its specified supply temperature in which case a heating coil 29 (heating heat exchanger) is used to raise the air temperature to its specified supply set point temperature. The heating coil 29 is a condenser in the second cooling coil refrigerant circuit 73 as more fully described below.

Located in passage 14 downstream of the first cooling coil 27 is a thermostat 31 to measure the temperature of the air exiting the first cooling coil. Located in passage 16 downstream of the heat exchanger wall 26 is a dew point temperature thermostat 32 to measure the dew point of the air exiting the second cooling coil 28. Located in passage 17 downstream of the fan 19 and the heating coil 29 is a thermostat 33 to measure the temperature of the air exiting the dehumidifier apparatus. A pressure gage 35 measures the differential pressure across the fan 19 in order to calculate the air speed and hence volume of air delivered by the fan. The controller 30 communicates with each of the thermostats and pressure gage so as to receive information therefrom, to be used in controlling the dehumidifier assembly 10.

If the first cooling coil 27 is a water cooled coil, the connecting cold water pipework to the first cooling coil 27 has a modulating water valve 34 to control the flow of water so as to regulate the air temperature leaving the first cooling coil 27.

If the first cooling coil 27 is an evaporator in a first refrigerant circuit, this first refrigerant circuit 73 is depicted in FIG. 2.

The first refrigeration circuit 73 includes a refrigerant compressor 61 which is a variable speed compressor controlled by a variable speed drive 69 which communicates with the controller 30, to vary the rotational speed of the compressor 61 and hence the refrigeration capacity of the first refrigerant circuit 73. The compressor 61 discharges hot high pressure refrigerant gas into a hot gas pipe 62 which delivers hot refrigerant gas to be cooled by air in a refrigerant condenser 63. Condenser fan 70 in the first refrigeration circuit 73 causes air to flow over the condenser coil 63 removing the heat gained in the first refrigeration circuit 73 to a location external from the dehumidification apparatus 10.

In another preferred form, the refrigerant condenser 63 is a water cooled condenser using water to reject heat from this first refrigerant circuit 73 external to the apparatus.

The condensing pressure in the first refrigeration circuit 73 is measured by pressure gage 71 which communicates this pressure to the controller 30. The controller 30 causes the fan 70 to speed up or slow down until the required condensing pressure is achieved. Alternatively, the controller 30 causes a modulating valve in the water cooled condenser to vary in capacity until the required condensing pressure is achieved.

Liquid refrigerant leaving condenser coil 63 is directed to an electronic expansion valve 65 through the liquid line pipe 64. The electronic expansion valve 65 causes the refrigerant pressure to drop such that it can evaporate and absorb heat from the evaporator coil 27 in the dehumidifier assembly. Air drawn over coil 27 is cooled to its set dew point temperature by losing heat to the refrigerant gas during the evaporation process. The superheat temperature of the gas leaving the coil 27 is measured by a thermostat 68 attached to the refrigerant suction line 66 transporting refrigerant from coil 27 to the suction accumulator 67 before it is returned to the compressor 61. The thermostat 68 communicates the refrigerant gas temperature in the gas line 66 to the controller 30. The controller 30 opens or closes the electronic expansion valve 65 until the refrigerant gas temperature in the gas line 66 is at a preset temperature.

The controller 30 causes the variable speed drive 69 to increase or decrease the rotational speed of the compressor 61 based on the air temperature recorded by temperature gage 31 in FIGS. 1&2 to maintain the air at a preset temperature.

The second air cooling coil 28 and the air heating coil 29 are an evaporator and a condenser respectively forming part of a second refrigeration circuit 74 as depicted in FIG. 3.

The second refrigeration circuit 74 includes a refrigerant compressor 41 which is a fixed speed compressor, discharging hot high pressure refrigerant gas into a hot gas pipe 42 which enters one port of an infinitely variable three way gas modulating valve 43. This infinitely variable three way gas modulating valve 43 can proportionally deliver hot refrigerant gas to heating coil 29 and refrigerant condenser 44 as directed by controller 30. Coil 29 is the air heating coil in the dehumidification assembly 10 and the volume of hot refrigerant gas directed to this coil 29 is determined by the amount of heat required, if any, to raise the temperature of the air exiting the heat exchanger 22 at wall 26 to its specified set point temperature. Heat surplus to that required to heat the air to its set point temperature generated in the second refrigeration circuit 74 is directed by the three way valve 43 to a the waste heat condenser 44 configured in parallel with condenser 29 to remove the surplus heat external to the dehumidification apparatus 10.

If there is a cold water source available, condenser 44 can be a water cooled condenser, discharging surplus heat via the chilled water cooling system. If there is no source of cold water available, condenser 44 is an air-cooled condenser discharging surplus heat to the external environment. Condenser 44 can form part of or be remote from the dehumidifier apparatus 10.

If condenser 44 is a water cooled condenser, there is a water modulating valve 51 that controls the flow of water to the water cooled condenser to regulate the rate of heat removal and hence the condensing pressure in the second refrigeration circuit 74. Alternatively, if the condenser 44 is an air cooled condenser, there is variable speed fan, or fans, 52 which moves air over the air cooled condenser 44 to remove heat from the refrigeration circuit 74 to the outside air. The fan speed is adjusted to regulate the rate of heat removal and hence the condensing pressure in the second refrigeration circuit 74.

The condensing pressure in the second refrigeration circuit 74 is measured by pressure gage 53 which communicates this pressure to the controller 30. The controller 30 causes either the water modulating valve 51 to open or close or the fan 52 to speed up or slow down until the required condensing pressure is achieved. The controller 30 controls the required condensing pressure in the second refrigeration circuit 74 to ensure that when additional air heating is required, the air exiting coil 29 is at the specified set point temperature when measured by thermostat 33.

Liquid refrigerant leaving condenser coils 29 and 44 is directed to an electronic expansion valve 46 through the liquid line pipe 45. The electronic expansion valve 46 causes the refrigerant pressure to drop such that it can evaporate and absorb heat from the coil 28. Air drawn over coil 28 is cooled to its set point temperature by losing heat to the refrigerant gas during the evaporation process. The superheat temperature of the gas leaving the coil 28 is measured by a thermostat 55 attached to the refrigerant suction line 47 transporting refrigerant from coil 28 to the suction accumulator 52 before it is returned to the compressor 41. The thermostat 55 communicates the refrigerant gas temperature in the gas line 47 to the controller 30. The controller 30 opens or closes the electronic expansion valve 46 until the refrigerant gas temperature in the gas line 47 is at a preset temperature.

The evaporating pressure in coil 28 must be maintained at a constant pre-determined pressure. This is achieved by injecting hot refrigerant gas to a point upstream of the coil 28 through the hot refrigerant gas bypass line 50. A two way modulating gas valve 49 is placed in the hot gas pipeline 50 to regulate the flow of hot gas so as to accurately control the hot gas flow rate and hence the refrigerant evaporating pressure in coil 28. The evaporating pressure is measured by the pressure gage 54 which communicates this pressure to the controller 30. Controller 30 causes the two way modulating valve 49 to open or close to maintain the preset evaporating pressure in coil 28.

In operation, the controller 30 is set to deliver a specific flow volume of air at a specified temperature and absolute humidity. The controller 30 has been programmed with algorithms that control the fan 19 speed, the evaporation pressure in coil 28, the dew point temperature of the air off the coil 28 and the air temperature off the heating coil 29 by:

-   -   a. causing modulation of the motorized damper 18;     -   b. a change in rotational speed of the variable speed compressor         61 in the first refrigeration circuit 73 to vary the         refrigeration capacity of the first refrigeration circuit 73 and         therefore air temperature off the coil 28;     -   c. maintaining a constant evaporating pressure in the second         refrigeration circuit to a preset level; and     -   d. varying the condensing pressure in the second refrigeration         circuit 74 to a pressure that will deliver the amount of heat         necessary to raise the temperature of the air off heating coil         29 to its present level;

Air is drawn by the fan 19 through the assembly 10, passing through passage 12, the heat exchanger first path 23-24, the second air passage 13, the coil 27, the third air passage 14, the coil 28, the fourth air passage 15, the heat exchanger 22 second path 25-26, the fifth air passage 16, the air heating coil 29 to exit the assembly 10 through the sixth air passage 17. The pressure gage 35 measures the differential pressure across the fan 19 sending the measurements to controller 30 which adjusts the fan speed until the required differential pressure is achieved indicating that the fan is supplying the specified air volume.

As the air passes through the heat exchanger first path 23-24, the air temperature will be lowered by the cold air passing through the heat exchanger second path 25-26, possibly below its dew point temperature causing water vapour to condense from the air and fall through the heat exchanger first path for collection into a drainage tray. The heat exchanger 22 efficiently precools and reheats the air reducing the refrigeration cooling load and therefore the amount of energy consumed in the dehumidification process.

As the air passes over the first cooling coil 27 its temperature is further lowered. The temperature of the air off the first cooling coil 27 is determined by the controller 30 based on the temperature measured by thermostat 32. The controller 30 will cause either:

-   -   a. in the case of a water cooled first cooling coil 27, the         water modulating valve 34 to open or close to achieve the         specified temperature of the air off the coil 28; or     -   b. in the case of the coil 27 being an evaporator in a first         refrigerant circuit, the operation of the first refrigerant         circuit 73 to deliver air off the coil 27 such that the air off         the coil 28 is at the specified air temperature.

Irrespective of the coil 27 cooling source, the air is cooled below its entering dew point to cause condensation to remove water vapour from the air. Cooling the air to an intermediate temperature that is between its temperature after exiting heat exchanger wall 24 and the final temperature to which it must be cooled to achieve the specified absolute humidity:

-   -   a. allows the use of chilled water to perform part of the         cooling load when it is available;     -   b. reduces the energy consumed in refrigeration cooling process         as the part of the cooling load performed by the coil 27 is done         at a higher efficiency or COP, whether by chilled water or         direct exchange refrigeration, because both are done at a higher         evaporating pressure.     -   c. reduces the water condensation performed on the low         temperature coil 28 to minimize ice formation; and     -   d. delivers air to the coil 28 at a temperature such that the         second refrigeration circuit 74 can maintain a constant         evaporating pressure to deliver air off the coil 28 at the         required dew point temperature and absolute humidity value.

The controller 30 has been programmed with evaporating pressures in the second refrigeration circuit 74 corresponding to specific absolute humidity levels. In operation, the controller 30 maintains the coil 28 pressure at the specified pressure corresponding to the preset specified absolute humidity.

As the air passes over the coil 28 its temperature is further lowered to the dew point temperature corresponding with the specified absolute humidity. The dew point temperature of the air is measured leaving the heat exchanger wall 26 by thermostat 32 as measurements performed in air passage 15 are inaccurate because of contamination by cold condensed water in this passage 15. If the dew point temperature measured by thermostat 32 is below the specified value, the controller 30 causes the air temperature off the coil 27 to rise by either:

-   -   a. adjusting the water modulating valve 34 to restrict water         flow to the coil 27; or     -   b. decreasing the rotational speed of the first refrigerant         circuit 73 compressor 61 to decrease the refrigeration capacity.

If the dew point temperature measured by thermostat 32 is above the specified value, the controller 30 causes the air temperature off the coil 27 to fall by either:

-   -   c. adjusting the water modulating valve 34 to increase water         flow to the coil 27; or     -   d. increasing the rotational speed of the first refrigerant         circuit compressor 61 to increase the refrigeration capacity.

The cold dry air exiting the coil 28 now passes through air passage 15 to the heat exchanger second path 25-26 where it is heated by the warmer moist air passing through the heat exchanger first path 23-24. The air temperature rises considerably as it has a very low absolute humidity and therefore requires less heat energy per degree of temperature increase. The heat transferred from the air in the first path of the heat exchanger 22 to the air in the heat exchanger second path causes its temperature to fall to a lesser degree than the temperature gained by the air in the heat exchanger second path because of the humidity difference in the two air streams.

If the air temperature measured by thermostat 33 is below the specified supply temperature, the controller 30 causes the three way modulating valve 43 in the second refrigeration circuit 74 to pass more hot gas refrigerant through the coil 29 to raise the temperature of the air to its specified level. This valve 43 will modulate to ensure the amount of hot gas refrigerant passing through coil 29 maintains the specified air supply temperature. The hot gas that is not required for this air heating is directed by the three way modulating valve 43 to the condenser 44 to be dissipated external to the dehumidifier.

In some instances, the air entering the first path 23-24 of the heat exchanger 22 is of sufficient heat and humidity to cause the air returning through the heat exchanger second path 25-26 to rise above its specified supply temperature when measured at thermostat 33. In this case the controller 30 causes the three way modulating valve 43 to direct all of the hot refrigerant gas to the condenser 44 to be dissipated external to the dehumidifier. The controller 30 causes the motorized damper 18 to open allowing a portion of the incoming air to bypass the heat exchanger first path 23-24 to be cooled directly on the coil 27. The volume of air passing through the heat exchanger second path is now greater than the volume of air passing through the heat exchanger first path. The amount of heat available in the heat exchanger first path to raise the temperature of the air in the heat exchanger second path has thus been reduced causing the air exiting the second path of the heat exchanger 22 at wall 26 to fall. The controller 30 causes the motorized damper 18 to modulate to ensure that the air temperature measured at thermostat 33 remains at its specified supply temperature. When the entry air temperature and/or humidity falls such that temperature of the air when measured at thermostat 33 falls below the specified supply temperature, the controller closes the motorized damper 18 and directs the three way valve 43 to operate as described above.

The dehumidifier apparatus 10 described herein efficiently lowers the absolute humidity of air by refrigeration without desiccant to a level below 5 gms/kg by cooling the air below the corresponding dew point. It uses a heat exchanger 22 to perform part of the necessary cooling reducing the refrigeration required, a coil 27 and a second coil 28 to lower the air temperature to its specified humidity dew point. It then reheats the cold dry air to the specified supply temperature in the heat exchanger 22 and uses waste condenser heat from the refrigeration process to further heat the air if it remains below its specified supply temperature when leaving the dehumidifier apparatus 10.

The dehumidifier apparatus 10 described herein can be an independent stand alone apparatus or incorporated within a larger air conditioning machine so as to mix the low dew point dehumidified air it produces with other air being returned from the enclosed space and then heated or cooled to deliver air at the specified temperature and humidity. 

1. A dehumidification apparatus including: a primary heat exchanger having a first air path and a second air path, with the heat exchanger providing for transfer of heat between air passing along the two paths; a first air passage that directs input air entering the dehumidifier into the heat exchanger; a second air flow passage that receives the input air after passing through the heat exchanger first path; an airflow regulator, operatively associated with the first air passage and upstream of the heat exchanger, to selectively direct at least part of the input air from the first air passage to the second air flow passage so that air so directed bypasses the heat exchanger; a first air cooling heat exchanger to which air is directed by the second air flow passage; a second air cooling heat exchanger; a third air flow passage that directs air leaving the first air cooling heat exchanger to the second air cooling heat exchanger; a fourth air flow passage that directs air leaving the second air cooling heat exchanger to the second air flow path of the heat exchanger; an air heating heat exchanger; a fifth air flow passage that directs the air leaving the second air flow path of the heat exchanger to the air heating heat exchanger; an air movement device that causes the air to pass through the dehumidifier from an air inlet to an air outlet, with the inlet delivering air to the first passage, and the outlet receiving air from the air heating heat exchanger; and a controller operatively associated with the air flow regulator, air movement device, first air cooling heat exchanger, second air cooling heat exchanger, and air heating heat exchanger, so that air leaving the air outlet has a required absolute humidity and temperature.
 2. The apparatus of claim 1, wherein the air movement device is a fan or fans located in the fifth or sixth air passage but downstream of the heat exchanger second path, each fan being operable to move air through the passages and heat exchanger paths.
 3. The apparatus of claim 1, wherein the airflow regulator is a motorised damper.
 4. The apparatus of claim 1, wherein the controller operates the air flow regulator to govern the flow rate of air delivered to the heat exchanger first path, and the second air flow passage.
 5. The apparatus of claim 1, wherein the first air cooling heat exchanger receives chilled water.
 6. The apparatus of claim 1, wherein the second air cooling heat exchanger is an evaporator in a refrigeration circuit.
 7. The apparatus of claim 1, wherein, the first air cooling heat exchanger is a refrigerant evaporator.
 8. The apparatus of claim 1, wherein the air heating heat exchanger is a refrigerant condenser.
 9. The apparatus of claim 1, wherein the assembly includes a refrigerant circuit including an evaporator providing the second air cooling heat exchanger, and a condenser providing the air heating heat exchanger.
 10. The apparatus of claim 9, wherein the refrigeration circuit includes a further condenser, arranged in parallel with the air heating heat exchanger to discharge excess heat from the apparatus.
 11. The apparatus of claim 1, wherein moisture is inhibited from passing between the two air paths in the heat exchanger.
 12. The apparatus of claim 1, wherein the second air cooling heat exchanger is mounted horizontally to aid in draining condensed water or specially constructed for vertical installation.
 13. The apparatus of claim 2, wherein the controller operates the air flow regulator to govern the flow rate of air delivered to the heat exchanger first path, and the second air flow passage.
 14. The apparatus of claim 13, wherein the first air cooling heat exchanger receives chilled water.
 15. The apparatus of claim 14, wherein the second air cooling heat exchanger is an evaporator in a refrigeration circuit.
 16. The apparatus of claim 15, wherein, the first air cooling heat exchanger is a refrigerant evaporator.
 17. The apparatus of claim 16, wherein the air heating heat exchanger is a refrigerant condenser.
 18. The apparatus of claim 17, wherein the assembly includes a refrigerant circuit including an evaporator providing the second air cooling heat exchanger, and a condenser providing the air heating heat exchanger.
 19. The apparatus of claim 18, wherein the refrigeration circuit includes a further condenser, arranged in parallel with the air heating heat exchanger to discharge excess heat from the apparatus.
 20. The apparatus of claim 19, wherein moisture is inhibited from passing between the two air paths in the heat exchanger, and the second air cooling heat exchanger is mounted horizontally to aid in draining condensed water or specially constructed for vertical installation. 